A previously well 14-year-old girl presented to the emergency department with a 2-day history of anorexia, nausea, abdominal distention, and lower abdominal pain increasing in severity. She denied fever and diarrhea but reported 1 episode of nonbilious emesis the day prior to presentation. She had never had abdominal surgeries, was not sexually active, and was 2 years postmenarche.

Results of her physical examination revealed a soft, tympanitic, mildly distended abdomen, tenderness in the lower quadrants, and a palpable, painful mass in the right lower quadrant. She had voluntary guarding but no rebound. The remainder of the examination was unremarkable. A plain radiograph of the abdomen was obtained (Figure).